Double gate transistor device and method of operating

ABSTRACT

In accordance with an embodiment, a method includes switching on a transistor device by generating a first conducting channel by driving a first gate electrode and, before generating the first conducting channel, generating a second conducting channel by driving a second gate electrode, wherein the second gate electrode is adjacent the first gate electrode in a current flow direction of the transistor device.

This application is a continuation in part based on U.S. patentapplication Ser. No. 15/056,392, filed on Feb. 29, 2016, entitled“Double Gate Transistor Device and Method of Operating”, whichapplication is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure in general relates to a transistor device, in particulara field-effect controlled power transistor device.

BACKGROUND

Field-effect controlled power transistor devices, such as power MOSFETs(Metal Oxide Field-Effect Transistors) or power IGBT's (Insulated GateBipolar Transistors) are widely used in automotive, industrial, orconsumer electronic applications for driving loads, converting power, orthe like. Such power transistors are available with voltage blockingcapabilities of between several 10 volts (V) and several kilovolts (kV)and current ratings of between several amperes (A) and severalkiloamperes (kA). The “voltage blocking capability” defines the maximumvoltage the transistor device can withstand in an off-state (whenswitched off), and the “current rating” defines a maximum current thetransistor device can conduct in the on-state (when switched on).

A field-effect controlled power transistor device switches on and offdependent on a voltage level of a drive voltage applied between a drivenode (often referred to as gate node) and a load node (often referred toas source node or emitter node). A normally-off device (enhancementdevice) is in the off state when the drive voltage is zero so that adevice of this type can be switched off by setting the drive voltage tozero. In operation of a power transistor device parasitic voltage spikesmay occur at the gate node when the transistor device is in theoff-state. Those voltage spikes may result from rapid changes ofcurrents through parasitic inductances, such as line inductances; rapidcurrent changes may result from switching operations of other powertransistors in a circuit where the power transistor is employed.

There is a need to provide a transistor device that is robust againstparasitic voltage spikes and can be controlled (switched on and off) inan efficient way, and a method for operating such transistor device inan efficient way.

SUMMARY OF THE INVENTION

One example relates to a method. The method includes switching on atransistor device by generating a first conducting channel by driving afirst gate electrode and, before generating the first conductingchannel, generating a second conducting channel by driving a second gateelectrode. The second gate electrode is adjacent the first gateelectrode in a current flow direction of the transistor device.

Another example of a method includes switching off a transistor deviceby interrupting a first conducting channel by driving a first gateelectrode and, after interrupting the first conducting channel,interrupting a second conducting channel by driving a second gateelectrode. The second gate electrode is arranged adjacent the first gateelectrode in a current flow direction of the transistor device.

Another example relates to a transistor device with at least onetransistor cell. The wherein the at least one transistor cell includes adrift region, a body region, a source region and a drain region, whereinthe body region is arranged between the source region and the driftregion, and wherein the drift region is arranged between body region andthe drain region. A gate electrode is dielectrically insulated from thebody region by a first gate dielectric, and a second gate electrode isdielectrically insulated from the body region by a second gatedielectric, arranged adjacent the first gate electrode, and separatedfrom the first gate electrode by a separation layer.

A transistor device according to another example includes asemiconductor body with a first semiconductor layer and a secondsemiconductor layer adjoining the first semiconductor layer. The firstsemiconductor layer includes a first type of group III nitride, and thesecond semiconductor layer includes a second type group III nitride. Asource electrode is connected to the first semiconductor layer and thesecond semiconductor layer, a drain electrode is spaced apart from thesource electrode and connected to the first semiconductor layer and thesecond semiconductor layer, and a first gate electrode and a second gateelectrode that are spaced apart in a current flow direction of thetransistor device.

One example relates to a method. The method includes switching on atransistor device by generating a first conducting channel in a bodyregion by driving a first gate electrode and, before generating thefirst conducting channel, generating a second conducting channel in thebody region by driving a second gate electrode. The first gate electrodeis dielectrically insulated from a body region by a first gatedielectric. The second gate electrode is dielectrically insulated fromthe body region by a second gate dielectric, arranged adjacent to thefirst gate electrode, and separated from the first gate electrode by aseparation layer, and the body region is arranged between a sourceregion and a drift region, and wherein the drift region is arrangedbetween body region and a drain region.

One example relates to a method. The method includes switching off atransistor device by interrupting a first conducting channel in a bodyregion by driving a first gate electrode and, after interrupting thefirst conducting channel, interrupting a second conducting channel inthe body region by driving a second gate electrode. The first gateelectrode is dielectrically insulated from a body region by a first gatedielectric. The second gate electrode is dielectrically insulated fromthe body region by a second gate dielectric, arranged adjacent the firstgate electrode, and separated from the first gate electrode by aseparation layer. The body region is arranged between a source regionand a drift region, and wherein the drift region is arranged betweenbody region and a drain region.

One example relates to a method. The method includes driving a firstgate electrode of a transistor device and monitoring at least oneelectrical parameter of a second gate electrode of the transistordevice. The first gate electrode is dielectrically insulated from a bodyregion by a first gate dielectric. The second gate electrode isdielectrically insulated from the body region by a second gatedielectric, arranged adjacent the first gate electrode, and separatedfrom the first gate electrode by a separation layer. The body region isarranged between a source region and a drift region, and wherein thedrift region is arranged between body region and a drain region.

Another example relates to a transistor device. The transistor deviceincludes at least one transistor cell. The at least one transistor cellincludes a drift region, a body region, a source region and a drainregion. The body region is arranged between the source region and thedrift region, and the drift region is arranged between body region andthe drain region. The transistor device further includes a first gateelectrode dielectrically insulated from the body region by a first gatedielectric, and a second gate electrode. The second gate electrode isdielectrically insulated from the body region by a second gatedielectric, is arranged adjacent the first gate electrode, and isseparated from the first gate electrode by a separation layer.

Another example relates to a drive circuit. The drive circuit includesan input configured to receive an input signal a first output configuredto be coupled to a first gate node of a transistor device, and a secondoutput configured to be coupled to a second gate node of a transistordevice configured to. The drive circuit is configured to drive the firstgate node and the second gate node based on the input signal, and todetect an operation state of the transistor device based on monitoringat least one electrical parameter at the second output.

Yet another example relates to a drive circuit. The drive circuitincludes an input configured to receive an input signal, a first outputconfigured to be coupled to a first gate node of a transistor device,and a second output configured to be coupled to a second gate node of atransistor device. The drive circuit is configured to operate in adiagnostic mode, wherein in the diagnostic mode, the transistor deviceis configured to diagnose the transistor device based on driving thefirst gate node via the first output and monitoring at least oneelectrical parameter at the second output.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples are explained below with reference to the drawings. Thedrawings serve to illustrate certain principles, so that only aspectsnecessary for understanding these principles are illustrated. Thedrawings are not to scale. In the drawings the same reference charactersdenote like features:

FIG. 1 shows a vertical cross-sectional view of one transistor cell of adouble gate transistor device according to one example;

FIG. 2A shows the circuit symbol of a double gate transistor deviceimplemented as an IGBT;

FIG. 2B shows the circuit symbol of a double gate transistor deviceimplemented as a MOSFET;

FIG. 3 shows a vertical cross-sectional view of one section of a doublegate transistor device including a plurality of parallel connectedtransistor cells;

FIG. 4 shows a perspective sectional view of one transistor cell of adouble gate transistor device according to one example;

FIG. 5 shows an electronic circuit that illustrates the use of a doublegate transistor device as an electronic switch;

FIG. 6 shows timing diagrams that illustrate one example of how a doublegate transistor device can be switched on;

FIG. 7 shows timing diagrams that illustrate another example of how adouble gate transistor device can be switched on;

FIG. 8 shows a modification of one of the timing diagrams shown in FIGS.6 and 7;

FIG. 9 shows another modification of one of the timing diagrams shown inFIGS. 6 and 7;

FIG. 10 shows one example of a driver stage configured to switch on adouble gate transistor device;

FIG. 11 shows another example of a driver stage configured to switch ona double gate transistor device;

FIG. 12 shows yet another example of a driver stage configured to switchon a double gate transistor device;

FIG. 13 shows timing diagrams that illustrate one example of how adouble gate transistor device can be switched off;

FIG. 14 shows timing diagrams that illustrate another example of how adouble gate transistor device can be switched off;

FIG. 15 shows a modification of one of the timing diagrams shown inFIGS. 13 and 14;

FIG. 16 shows another modification of one of the timing diagrams shownin FIGS. 13 and 14;

FIG. 17 shows one example of a driver stage configured to switch off adouble gate transistor device;

FIG. 18 shows another example of a driver stage configured to switch offa double gate transistor device;

FIG. 19 shows yet another example of a driver stage configured to switchoff a double gate transistor device;

FIG. 20 shows one example of a driver that includes a first driverstage, a second driver stage and a detection circuit;

FIG. 21 shows one example of the detection circuit in greater detail;

FIG. 22 shows timing diagrams that illustrate operation of the detectioncircuit shown in FIG. 21;

FIG. 23 shows an equivalent circuit diagram of a double gate transistordevice; and;

FIGS. 24 and 25 show signal diagrams illustrating one way of operationof the detection circuit shown in FIG. 22;

FIG. 26 shows the circuit symbol of a double gate transistor implementedas a HEMT (High Electron Mobility Transistor);

FIG. 27 shows a vertical cross sectional view of a HEMT according to oneexample;

FIGS. 28 and 29 show timing diagrams that illustrate one example of howthe HEMT shown in FIG. 27 can be switched on and off, respectively;

FIG. 3o shows vertical cross sectional view of a HEMT according toanother example;

FIG. 31 shows a modification of the HEMT shown in FIG. 30;

FIG. 32 shows a vertical cross sectional view of a GIT (Gate InjectionTransistor) according to one example;

FIG. 33 shows a modification of the GIT shown in FIG. 32; and

FIG. 34 shows one example of how lines between a driver, a source andtwo gate node of a double gate transistor device may be arranged.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings. The drawings form a part of the description andby way of illustration show specific embodiments in which the inventionmay be practiced. It is to be understood that the features of thevarious embodiments described herein may be combined with each other,unless specifically noted otherwise.

FIG. 1 shows a vertical cross sectional view of one transistor cell of adouble gate transistor device according to one example. The transistorcell includes a drift region 11, a body region 12, a source region 13and a drain region 14. The body region 12 is arranged between the driftregion 11 and the source region 13, and the drift region 11 is arrangedbetween the body region 12 and the drain region 14. These regions, whichmay briefly be referred to as active device regions, are dopedsemiconductor regions arranged in a semiconductor body 100. Thesemiconductor body 100 may include a conventional semiconductor materialsuch as, for example, silicon (Si), silicon carbide (SiC), galliumarsenide (GaAs), gallium nitride (GaN), or the like.

Referring to FIG. 1, the transistor cell further includes a first gateelectrode 21 dielectrically insulated from the body region 12 by a firstgate dielectric 22, and a second gate electrode 31 dielectricallyinsulated from the body region 12 by a second gate dielectric 32. Thesecond gate electrode 31 is arranged adjacent the first gate electrode21 and is separated from the first gate electrode 21 by a separationlayer 23. The first gate electrode 21 is electrically connected to agate node G1, and the second gate electrode 31 is electrically connectedto a second gate node G2 different from the first gate node G1. Thesegate nodes G1, G2 are only schematically illustrated in FIG. 1.According to one example, the separation layer 23 includes a dielectriclayer. According to one example, the first gate dielectric 22, thesecond gate dielectric 32 and the separation layer 23 include the sametype of material such as, for example, an oxide, a nitride, anoxy-nitride, or the like.

The first gate dielectric 22 has a first thickness d₂₂, which defines ashortest distance between the first gate electrode 21 and the bodyregion 12, and the second gate dielectric 32 has a second thickness d₃₂,which defines the shortest distance between the second gate electrode 31and the body region 12. According to one example, these thicknesses d₂₂,d₃₂ are substantially equal, so that d₂₂=d₃₂. According to anotherexample, one of is less than twice of the other one of the firstthickness d₂₂ and the second thickness d₃₂, that is, 0.5≤d₂₂/d₃₂≤2.

Each of the first gate dielectric 22 and the second gate dielectric 32adjoins the body region 12. Furthermore, the first gate dielectric 22adjoins the source region 13 and the second gate dielectric 32 adjoinsthe drift region 11. Thus, the first gate electrode 21 is adjacent thesource region 13 additionally to being adjacent to the body region 12,and the second gate electrode 31 is adjacent the drift region 11additionally to being adjacent to the body region 12.

The transistor device can be implemented as an n-type transistor deviceor a p-type transistor device. The type of the transistor device isdefined by a doping type of the source region 13. The source region 13is n-doped in an n-type transistor device and p-doped in a p-typetransistor device. A doping type of the body region 12 is complementaryto the doping type of the source region 13, so that the body region 12is p-doped in an n-type transistor device and n-doped in a p-typetransistor device. A doping type of the drift region 11 equals thedoping type of the source region 13 and is complementary to the dopingtype of the body region 12, so that a pn-junction is formed between thebody region 12 and the drift region 11.

The transistor device can, for example, be implemented as an IGBT or asa MOSFET. In an IGBT a doping type of the drain region 14 iscomplementary to the doping type of the drift region 11 and the sourceregion, respectively, and in a MOSFET the doping type of the drainregion 14 equals the doping type of the drift region 11 and the sourceregion 13, respectively. Optionally, the transistor device includes afield-stop region 15 of the same doping type as the drift region 11between the drift region 11 and the drain region 14. A dopingconcentration of the field-stop region 15 is higher than the dopingconcentration of the drift region 11 and lower than the dopingconcentration of the drain region 14.

Further, the transistor device can be implemented as a normally-offdevice (enhancement device) or a normally-on device (depletion device).In a normally-off device, the body region 12 adjoins the gatedielectrics 22, 32. The normally-off device can be switched on or off bycontrolling an inversion channel in the body region 12 along the gatedielectrics. This is explained in further detail below. In a normally-ondevice, the body region 12 includes a channel region 17 (illustrated indashed lines in FIG. 1) of the same doping type as the source region 13and the drift region 11 that adjoins the gate dielectrics 22, 32. Thenormally-on device can be switched on or off by depleting or notdepleting the channel region 17. This is also explained in furtherdetail below.

For example, a doping concentration of the drift region 11 is selectedfrom a range of between 1E12 cm⁻³ and 1E15 cm⁻³, between 5E12 cm⁻³ and1E14 cm⁻³, or 7E12 cm⁻³ and 1E13 cm⁻³, a doping concentration of theoptional field-stop region 15 is selected from a range of between 1E15cm⁻³ and 1E16 cm⁻³, a doping concentration of the body region 12 isselected from a range of between 1E16 cm⁻³ and 5E18 cm⁻³, a dopingconcentration of the source region 13 is higher than 1E19 cm⁻³, and adoping concentration of the channel region may be selected from the samerange as the doping concentration of the body region 12. In a MOSFET, adoping concentration of the drain region 13 is higher than 1E18 cm⁻³ orhigher than 1E19 cm⁻³, for example. In an IGBT (where the drain region14 can also be referred to as collector region), a doping concentrationof the drain region 13 is higher than 1E17 cm⁻³ or higher than 1E18cm⁻³, for example. According to one example, the doping concentration ofthe drain region 14 is at least 1E3 times, 1E4 times, or at least 1E5times the doping concentration of the drift region 11.

The transistor cell shown in FIG. 1 is a vertical transistor cell. Thatis, the source region 13 and the drain region 14 are spaced apart in avertical direction of the semiconductor body 100. The “verticaldirection” of the semiconductor body 100 is a direction perpendicular toa first surface 101 of the semiconductor body 100. The first gateelectrode 21 and the second gate electrode 22 are located in one trenchthat extends from the first surface 101 into the semiconductor body 100.By this, the first gate electrode 21 and the second gate electrode 22are adjacent in the vertical direction of the semiconductor body 100,whereas the first gate electrode 21 is closer to the first surface 101than the second gate electrode 31. The method for driving a transistordevice however, is not restricted to be used in a vertical transistordevice, but may as well be used in a lateral transistor device. Alateral transistor device is a transistor device in which a drain regionand a source region are spaced apart in a lateral direction of asemiconductor body. The lateral direction is a direction parallel to a(main) surface of the semiconductor body.

FIG. 2A shows a circuit symbol of a double gate transistor deviceimplemented as an IGBT. This circuit symbol is based on the circuitsymbol of a conventional IGBT and is different from the circuit symbolof a conventional IGBT in that it includes two gate nodes, namely thefirst gate node G1 and a the gate node G2. FIG. 2B shows the circuitsymbol of a double gate transistor device implemented as a MOSFET. Thecircuit symbol shown in FIG. 2B is based on the circuit symbol of aconventional MOSFET and is different from the circuit symbol of aconventional MOSFET in that it includes two gate nodes, namely the firstgate node G1 and the second gate node G2. Just for the purpose ofillustration, the circuit symbols shown in FIGS. 2A and 2B are drawn torepresent n-type transistor devices.

According to one example, the transistor device includes a plurality oftransistor cells of the type shown in FIG. 1. FIG. 3 shows a verticalcross sectional view of one section of a transistor device that includesa plurality of such transistor cells. These transistor cells areconnected in parallel by having their first gate electrodes 21 connectedto one common first gate node G1, by having their second gate electrodes31 connected to a common second gate node G2, by having their sourceregions 13 electrically connected to a common source node S, and byhaving their drain regions 14 connected to a common drain node D. In theembodiment shown in FIG. 3, the drain regions of the individualtransistor cells are formed by one common drain region 14 connected tothe drain node D. Furthermore, the drift regions of the individualtransistor cells are formed by one common drift region 11.

According to one example, the source regions 13 and the body regions 12of the individual transistor cells are connected to the source node S.Referring to FIG. 3, the body regions 12 may include contact regions 16connected to the source node S. These contact regions 16 have the samedoping type as the body regions 12, are more highly doped than the bodyregions 12, and may provide an ohmic connection between the source nodeS and the body region 12.

In FIGS. 1 and 3, connections between the second gate electrode 31 andthe second gate node G2 are only schematically illustrated. FIG. 4 showsa perspective sectional view of one transistor cell to illustrate howthe second gate electrode 31 may be connected to the second gate nodeG2. In the embodiment shown in FIG. 4, a section of the second gateelectrode 31 extends to the first surface 101 of the semiconductor body100. By this, the second gate electrode 31, like the first gateelectrode 21, can be contacted at the first surface 101 of thesemiconductor body 100. In a region where the second gate electrodes 31extend to the surface 101, the second gate electrode 31 is insulatedfrom the first gate electrode 21 by a further separation layer 24. Thisfurther separation layer 24 may include the same type of material as thefirst gate dielectric 22, the second gate dielectric 32 and theseparation layer 23. A thickness, which defines the shortest distancebetween the first gate electrode 21 and the second gate electrode 31, isgreater than the first thickness d₂₂ of the first gate dielectric 22 andthe second thickness d₃₂ of the second gate dielectric 32, for example.

The double gate transistor device explained above can be used as anelectronic switch. FIG. 5 shows a circuit diagram that illustrates oneexample of how the double gate transistor device can be used as anelectronic switch. Just for the purpose of illustration the double gatetransistor device is drawn as an IGBT (as shown in FIG. 2A) in thecircuit diagram shown in FIG. 5. In the circuit shown in FIG. 5, thetransistor device is connected in series with a load Z (illustrated indashed lines). In particular, the drain-source path D-S, which is aninternal path of the transistor device between the drain node D and thesource node S, is connected in series with the load Z. This seriescircuit with the transistor device and the load Z receives a supplyvoltage V+ which is available between a first supply node and a secondsupply node (ground node, GND), for example. The transistor device canbe switched on and switched off. When the transistor device is switchedon (is in the on-state) a current can flow via the drain-source path D-Sand, therefore, through the load Z. When the transistor device isswitched off (is in the off-state) it prevents a current to flow via thedrain-source path D-S and, therefore, through the load Z. Examples ofhow the transistor device can be switched on and switched off areexplained below.

Referring to FIG. 5, the double gate transistor device can be controlled(driven) by a drive circuit 5. This drive circuit 5 receives an inputsignal S_(IN) and is connected to the first gate node G1 and the secondgate node G2. According to one example, the drive signal S_(IN) can havetwo different signal levels, an on-level indicating that the transistordevice is to be switched on, and an off-level indicating that thetransistor device is to be switched off. The drive circuit 5 isconfigured to drive the transistor device in accordance with the inputsignal S_(IN). According to one example, the drive circuit 5 includes afirst driver stage 5 ₁ (illustrated in dashed lines in FIG. 5)configured to switch on the transistor device, and a second driver stage5 ₂ (illustrated in dashed lines in FIG. 5) configured to switch off thetransistor device. Examples of these driver stages 5 ₁, 5 ₂ areexplained with reference to drawings herein further below.

The double gate transistor device explained above is avoltage-controlled transistor device that switches on and off dependenton two drive voltages, namely a first drive voltage V_(G1S) and a seconddrive voltage V_(G2S). Referring to FIG. 5, the first drive voltageV_(G1S) is a voltage between the first gate node G1 and the source nodeS, and the second drive voltage V_(G2S) is a voltage between the secondgate node G2 and the source node S. Each of these voltages controls aconducting channel in the body region 12. The first drive voltageV_(G1S) controls a first conducting channel in the body region 12 alongthe first gate dielectric 22 and the second drive voltage V_(G2S)controls a second conducting channel in the body region 12 along thesecond gate dielectric 32. These conducting channels are field-effectcontrolled channels. According to one example, these conducting channelsare inversion channels in a normally-off device and accumulationchannels in a normally-on device. The transistor device is in theon-state when there is a continuous conducting channel in the bodyregion 12 along the first gate dielectric 22 and the second gatedielectric 22 between the source region 13 and the drift region 11.According to one example, if the transistor device is a normally-offdevice, the separation layer 23 is thin enough for the first conductingchannel and the second conducting channel to overlap in the region ofthe separation layer 23 so that there can be continuous conductingchannel in the body region 12 between the source region 13 and the driftregion 11.

Referring to FIGS. 1, 3, and 4, none of the first gate electrode 21 andthe second gate electrode 31 completely extends in a current flowdirection of the transistor device from the source region 13 to thedrift region 11 adjacent the body region 12. The “current flowdirection” is a direction in which a current can flow through thetransistor device between the source region 13 and the drain region 14when the transistor device is in the on-state. In the examples shown inFIGS. 1, 3, and 4, the current flow direction of the transistor deviceis the vertical direction of the semiconductor body 100 (the verticaldirection is the direction perpendicular to the first surface 101). Inthe current flow direction, the first gate electrode 21 is spaced apartfrom the drift region 11, and the second gate electrode 31 is spacedapart from the source region 13. Thus, the transistor device is only inthe on-state when first drive voltage V_(G1S) generates the firstconducting channel along the first gate dielectric 22 and the seconddrive voltage V_(G2S) generates the second conducting channel along thesecond gate dielectric 32. “To generate the conducting channel” mayinclude to generate an inversion channel in a normally-off device or notto interrupt the conducting channel by not depleting the channel region17 in a normally-on device. Consequently, the transistor device is inthe off-state when at least one of these first and second conductingchannels is interrupted.

FIG. 6 shows timing diagrams that illustrate one example of how thedouble gate transistor device can be driven from the off-state to theon-state. FIG. 6 shows timing diagrams of the input signal S_(IN), thesecond drive voltage V_(G2S), the first drive voltage V_(G1S), and thedrain-source voltage V_(DS) of the double gate transistor device.Referring to the above, switching on the transistor device includesgenerating the first conducting channel in the body region 12 along thefirst gate dielectric 22 and generating the second conducting channel inthe body region 12 along the second gate dielectric 32. In the methodillustrated in FIG. 6, the second conducting channel is generated beforethe first conducting channel is generated. Generating the secondconducting channel includes changing the second drive voltage V_(G2S)from an off-level V_(OFF2) to an on-level V_(ON2). Just for the purposeof illustration, the off-level V_(OFF2) is a negative level in theexample shown in FIG. 6 and the on-level V_(ON2) is a positive voltagelevel. This is applicable to an n-type double gate transistor device,and is applicable to a normally-off device and a normally-on device,wherein in a normally-on device the off-level may be chosen to be morenegative than in a normally-off device. The off-level V_(OFF2) is suchthat the second conducting channel in the body region 12 is safelyprevented when the second drive voltage V_(G2S) has the off-levelV_(OFF2), and the on-level V_(ON2) is such that there is the secondconducting channel in the body region 12 when the second drive voltageV_(G2S) has the on-level V_(ON2).

In FIG. 6, V_(TH2) denotes a threshold voltage associated with thesecond drive voltage V_(GS2). When the second drive voltage V_(G2S)reaches the threshold V_(TH2), which is between the off-level V_(OFF2)and the on-level V_(ON2), the second conducting channel starts toconduct. Increasing the second drive voltage V_(G2S) to above thethreshold V_(TH2), as shown in FIG. 6, may help to increase aconductivity of the second conducting channel and, therefore, decreasethe on-resistance of the transistor device in the on-state. The“on-resistance” of the transistor device is the electrical resistance ofthe transistor device between the drain node D and the source node S inthe on-state. In FIG. 6, the threshold V_(TH2) is drawn to be positive.This applies to an n-type normally-off type and is only an example. Inan n-type normally-on device, for example, the threshold V_(TH2) is zeroor negative.

Referring to FIG. 6, generating the second conducting channel mayinclude rapidly increasing the voltage level of the second drive voltageV_(G2S) from the off-level V_(OFF2) to the on-level V_(ON2). This isschematically illustrated by the second drive voltage V_(G2S) jumpingfrom the off-level V_(OFF2) to the on-level V_(ON2) at a first time t1.For example, t1 is the time when a signal level of the input signalS_(IN) changes from the off-level to the on-level. Just for the purposeof illustration, in FIG. 6, the off-level of the input signal S_(IN) isdrawn as a low level and the on-level is drawn as high level. The curveof the second drive voltage V_(GS2) shown in FIG. 6 is an idealisticcurve, which is for illustration purposes. In a real circuit there maybe delays and a less rapid increase of the second drive voltage V_(G2S).Nevertheless, the second drive voltage V_(G2S) can be increased as fastas possible and with no need to control such increase. The reason forthis is as follows: In a conventional transistor device a rapid increaseof the gate-source voltage may be critical as such rapid increase maycause rapid changes of the drain-source voltage and a current throughthe transistor device, respectively. Such rapid changes may causeundesirable electromagnetic interferences (EMI). The transistor deviceshown in FIGS. 1, 3, and 4 is still in the off-state after the secondconducting channel has been generated. Thus generating the secondconducting channel does not affect the drain-source voltage or thecurrent through the transistor device. Thus a rapid increase of thesecond drive voltage V_(G2S) to generate the second conducting channelis not critical in view of EMI.

In a circuit of the type shown in FIG. 5, the drain-source voltageV_(DS) substantially equals the supply voltage V+ when the transistordevice is in the off-state. Referring to FIG. 6, the drain-sourcevoltage V_(DS) remains at the level of the supply voltage V+ after thesecond drive voltage V_(G2S) has reached the on-level V_(ON2). Thisindicates that the transistor device is still in the off-state after thesecond conducting channel has been generated.

Generating the first conducting channel in the body region 12 includeschanging a voltage level of the first drive voltage V_(G1S) from anoff-level V_(OFF1) to an on-level V_(ON1). The off-level V_(OFF1) issuch that it prevents the first conducting channel from being generatedin the body region 12, and the on-level V_(ON1) is such that itgenerates the first conducting channel in the body region 12. Accordingto one example, the on-level V_(ON1) of the first drive voltage V_(G1S)equals the on-level V_(ON2) of the second drive voltage V_(G2S), so thatV_(ON1)=V_(ON2). According to one example, these voltage levels areselected from a range of between 5 V and 15 V. According to one example,the off-level V_(OFF1) of the first drive voltage V_(G1S), which isreferred to as first off-level in the following, is different from theoff-level V_(OFF2) of the second drive voltage, is referred to as secondoff-level in the following. According to one example, the transistordevice is a normally-off device, the first off-level V_(OFF1) issubstantially zero, and the second off-level V_(OFF2) is negative.According to another example, the transistor device is a normally-ondevice, and the first off-level V_(OFF1) is also negative. According toone example, the second off-level V_(OFF2) is selected from a range ofbetween 0 V and −15 V, in particular between −1V and −10V.

In FIG. 6, V_(TH1) denotes a threshold voltage associated with the firstdrive voltage V_(GS1). When the first drive voltage V_(G1S) reaches thelevel of the threshold V_(TH1), which will be referred to as firstthreshold V_(TH1) in the following, the first conducting channel isgenerated in the body region 12. In FIG. 6, t2 denotes a time when thefirst drive voltage V_(G1S) reaches the first threshold V_(TH1). As thesecond conducting channel has been generated before the first drivevoltage V_(G1S) reaches the first threshold _(TH1), t2 is the time whenthe double gate transistor device starts to conduct (switch on). Thus,beginning at the time t2, the drain-source voltage V_(GS) begins todecrease and the load-path voltage V_(Z) (which is given by the supplyvoltage V+ minus the drain-source voltage V_(DS)) starts to increase.The latter, however, is not shown in FIG. 6.

In the double gate transistor device, the rate at which the drain-sourcevoltage V_(DS) decreases and a current I_(DS) (see FIG. 5) through thetransistor device increases is substantially governed by the increase ofthe first drive voltage V_(G1S) after the first drive voltage V_(G1S)has reached the first threshold V_(TH1). The faster the first drivevoltage V_(G1S) increases, the faster the drain-source voltage V_(DS)decreases and the drain-source current I_(DS) increases, respectively.Thus, slopes of transients of the drain-voltage V_(DS) and thedrain-source current I_(DS) can be controlled by controlling theincrease of the first gate-source voltage V_(G1S).

Unlike a conventional field-effect controlled transistor device thedouble gate transistor device, when driven in accordance with the drivescheme explained above, exhibits substantially no Miller effect.According to the Miller effect, an increase of the gate-source voltageof a conventional transistor device is delayed after the gate-sourcevoltage reaches the threshold voltage. The reason for this is that thereis a parasitic gate-drain capacitance between the gate electrode and thedrain node of a conventional field-effect controlled transistor device.In the double-gate transistor device there is corresponding parasiticcapacitance between the second gate electrode 31 and the drain node D.This parasitic capacitance can be rapidly charged/discharged via thesecond gate node G2, as will be explained in further detail hereinbelow. The second gate electrode 31 shields the first gate electrode 21towards the drain region so that there is only a very small, if any,parasitic capacitance between the first gate electrode 21 and the drainregion 14. Thus, there is substantially no Miller effect involved ingenerating (controlling) the first conducting channel along the firstgate dielectric 22. Thus, electrical charge provided to the first gateelectrode 21 via the first gate node G1 only serves to generate thefirst conducting channel in the body region 12 but is not used tocharge/discharge parasitic capacitances such as the gate-draincapacitance. By virtue of this, charging/discharging the first gateelectrode can be precisely controlled, so that a switching on/switchingoff behavior of the double gate transistor can be precisely controlled.

In the example shown in FIG. 6, the first drive voltage V_(G1S) and thesecond drive voltage V_(G2S) start substantially at the time t1.According to another example, shown in FIG. 7, there is a delay time Δt1between the time when the second drive voltage V_(G2S) starts toincrease and the time when the first drive voltage V_(G1S) starts toincrease. For example, a time t1−Δt1 when the second drive voltageV_(G2S) starts to increase is the time when the input signal changesfrom the off-level to the on-level. The other explanations provided withregard to FIG. 6 apply to the example shown in FIG. 7 equivalently.

Referring to the explanation above, the second gate electrode 31 isadjacent the body region 12, separated from the body region 12 by thesecond gate dielectric 32, and configured to control the secondconducting channel in the body region 12. The second gate electrode 31may extend into the drift region 11. In this case, the second gateelectrode 31 is dielectrically insulated from the drift region 11 by adielectric layer 33. A thickness of this dielectric layer 33, whichdefines a shortest distance between the second gate electrode 31 and thedrift region 11, may correspond to the second thickness d₃₂ of thesecond gate dielectric or be greater than the second thickness d₃₂. Thatis, d₃₃≥d₃₂, wherein d₃₃ denotes the thickness of the further dielectriclayer 33. In FIG. 1, o₃₁ denotes an overlap between the second gateelectrode 31 and the body region 12. This overlap o₃₁ defines a length,in the current flow direction, of a section of the second gate electrode31 that is adjacent the body region 12. When the transistor device is inthe off-state and a voltage is applied between the drain node D and thesource node S, a space charge region (depletion region) expands in thedrift region 11 and the body region 12 beginning at the pn-junctionbetween the drift region 11 and the body region 12. According to oneexample, a doping concentration of the body region 12 and the overlapo₃₁ are designed such that the space charge region in the body region 12does not extend beyond the second gate electrode 31. That is, the spacecharge region does not extend farther in the direction of the firstsurface 101 than the second gate electrode 31. In this case, thetransistor device can be switched off by suitably driving the secondgate electrode 31, independent of the first drive voltage V_(G1S). Forexample, the overlap o₃₁ is selected from a range of between 0.5 m and 5m, in particular between 1 μm and 3 μm.

In the examples shown in FIGS. 6 and 7 the first drive voltage V_(G1S)is generated to increases substantially linearly beginning at the timet1. This, however, is only an example. According to another exampleshown in FIG. 8, the first drive voltage V_(G1S) is generated such thatit increases non-linearly. For example, the increase is such that itslows down as the level of the first drive voltage V_(G1S) approachesthe on-level V_(ON1).

According to yet another example, shown in FIG. 9, the increase of thefirst drive voltage V_(G1S) has two substantially linear sections, afirst section beginning at t1, and a second section following the firstsection. According to one example, the increase in the first section isslower than the second section.

FIG. 10 shows one example of the first driver stage 5 ₁ configured toswitch on the double gate transistor device. This first driver stage 5 ₁includes a first driver 51 ₁ configured to drive the first gate node G1(generate the first drive voltage V_(G1S) at the first gate node G1) anda second driver 52 ₁ configured to drive the second gate node G2(generate the second drive voltage V_(G2S) at the second gate node G2).A control circuit 53 ₁ receives the input signal S_(IN) and controlsoperation of the first driver 51, and the second driver 52 ₁ based onthe input signal S_(IN). In the example shown in FIG. 10, the seconddriver 52 ₁ includes a switch 521 ₁ coupled between the second gate nodeG2 and a supply node where a voltage having the second on-level V_(ON2)is available. This voltage is referenced to the source node S. The firstdriver 51 ₁ includes a switch 511 ₁ and a current source 512 ₁ connectedin series with the switch 511 ₁. The series circuit with the switch 511₁ and the current source 512 ₁ is connected between the first gate nodeG1 and a supply node where a voltage having the first on-level V_(ON1)is available. This voltage is also referenced to the source node S.

The first driver stage 5 ₁ shown in FIG. 10 is configured to drive thedouble gate transistor device in accordance with the timing diagramsshown in FIG. 6 or 7. In order to switch on the transistor device, thecontrol circuit 53 ₁ based on the input signal S_(IN) closes the switch521 ₁ in the second driver 52 ₁ and the switch 511 ₁ in the first driver51 ₁. When the switch 521 ₁ in the second driver 52 ₁ closes, the seconddrive voltage V_(G2S) rapidly increases to the second on-level V_(ON2)(as shown at times t1 and t1−Δt1 in FIGS. 6 and 7, respectively). Whenthe switch 511 ₁ of the first driver 51 ₁ closes, the first drivevoltage V_(G1S) increases substantially linearly (as shown at times t1in FIGS. 6 and 7, respectively), wherein a rate of the increase isdefined by a current level of a current I512 ₁ provided by the currentsource 512 ₁.

According to one example, the control circuit 53 ₁ is configured toclose the switches 511 ₁, 521 ₁ at the same time when the input signalS_(IN) indicates that it is desired to switch on the transistor device.In this case, the transistor device switches on in accordance with thetiming diagrams shown in FIG. 6. According to another example, thecontrol circuit 53 ₁ is configured to first switch on the switch 521 ₁in the second driver 52 ₁ and then switch on the switch 511 ₁ in thefirst driver 51 ₁. In this case, the transistor device switches on inaccordance with the timing diagrams shown in FIG. 7.

The first driver 51 ₁ and the second driver 52 ₁ can be optimized fordifferent purposes. According to one example, the second driver 52 ₁ isoptimized to rapidly charge the second gate electrode 31 via the secondgate node G2. For this, the second driver 52 ₁ may be configured todrive a high current into the second gate node G2. The first driver 51 ₁may be configured to charge the first gate electrode 21 via the firstgate node G1 in a predefined fashion. For this, as shown in FIG. 10, thefirst driver 51 ₁ may provide a drive current with a predefined currentlevel. According to one example, this current level is lower than acurrent level of a maximum drive current provided by the second driver52 ₁. According to one example the currents provided by the first andsecond drivers 51 ₁, 52 ₁ become zero when the respective drive voltageV_(G1S), V_(G2S) reaches a predefined voltage level. This is illustratedin FIGS. 6 and 7 in that the drive voltages V_(G1S), V_(G2S) do notfurther increase when they reach the first on-level V_(ON1) and thesecond on-level V_(ON2), respectively.

FIG. 11 shows another example of the first driver stage 5 ₁. This firstdriver stage 5 ₁ is based on the first driver stage 5 ₁ shown in FIG. 10and is different from the driver stage 5 ₁ shown in FIG. 10 in that thefirst driver 51 ₁ includes a resistor 513 ₁ instead of the currentsource 512 ₁. Using this first driver stage 5 ₁ a behavior of the firstdrive voltage V_(G1S) as shown in FIG. 8 can be obtained. The controlcircuit 53 ₁, like the control circuit 53 ₁ explained with reference toFIG. 10, may switch on the switches 521 ₁, 511 ₁ in the second driver 52₁ and the first driver 51 ₁, respectively, at the same time or with atime delay Δt1.

FIG. 12 shows another example of the first driver stage 5 ₁. This driverstage 5 ₁ is based on the driver stage 5 ₁ shown in FIG. 10 and isdifferent from the first driver stage 5 ₁ shown in FIG. 10 in that thefirst driver 51 ₁ includes a crossover switch 514 ₁ instead of anon/off-switch and two current sources 515 ₁, 516 ₁ instead of only onecurrent source 512 ₁. The crossover switch 514 ₁ is controlled by thecontrol circuit 53 ₁ and can have three different switching positions, afirst position, in which the crossover switch 514 ₁ connects the firstcurrent source 515 ₁ between the supply node and the first gate node G1;a second position, in which the crossover switch 514 ₁ connects thesecond current source 516 ₁ between the supply node and the first gatenode G1; and a third position, in which none of the current sources 515₁, 516 ₁ is connected between the supply node and the first gate nodeG1.

Using the first driver stage 5 ₁ shown in FIG. 12 a behavior of thefirst drive voltage V_(G1S) as shown in FIG. 9 can be obtained. When thetransistor device is in the off-state, the crossover switch 514 ₁couples none of the current source 515 ₁, 516 ₁ to the first gate nodeG1. When the transistor device is to be switched on, the crossoverswitch 514 ₁, controlled by the control circuit 53 ₁, connects the firstcurrent source 515 ₁ to the first gate node G1 at time t1, in order toobtain a first increase of the first drive voltage V_(G1S). After adelay time, the crossover switch 514 ₁ switches over to connect thecurrent source 516 ₁ to the first gate node G1, in order to obtain thesecond increase of the first drive voltage V_(G1S). A current providedby the second current source 516 ₁ can be higher than a current providedby the first current source 515 ₁ in order to obtain a timing diagram asshown in FIG. 9.

As an alternative to providing a crossover switch 514 ₁ a respectiveswitch (not shown) can be connected in series with each of the currentsources 515 ₁, 516 ₁. These switches can be controlled by the controlcircuit 53 ₁. In this example, the slower increase of the first drivevoltage V_(G1S) can be obtained by switching on only one of theswitches, and the faster increase can be obtained by switching on bothof the switches.

FIG. 13 shows timing diagrams of an example of how the double gatetransistor device can be switched from the on-state to the off-state. Inparticular, FIG. 13 shows timing diagrams of the input signal S_(IN),the first drive voltage V_(G1S), the second drive voltage V_(G2S), andthe drain-source voltage V_(DS).

Referring to the explanation above, the transistor device is in theon-state when there is the first conducting channel along the first gatedielectric 22 and the second conducting channel along the second gatedielectric 32. Switching off the transistor device includes interruptingthe first conducting channel before interrupting the second conductingchannel. Interrupting the first conducting channel includes decreasingthe first drive voltage V_(G1S) from the first on-level V_(ON1) to thefirst off-level V_(OFF1). In the example shown in FIG. 13, aswitching-off procedure of the transistor device starts at time t3 whenthe first drive voltage V_(G1S) starts to decrease. According to oneexample, this time t3 is defined by the input signal S_(IN) and may bethe time when the signal level of the input signal S_(IN) changes fromthe on-level to the off-level (whereas, for the purpose of illustration,propagation delays in the drive circuit 5 are neglected in the signaldiagrams shown in FIG. 13).

As the first drive voltage V_(G1S) decreases, the drain-source voltageV_(DS) increases. There may be a time delay between the time t3 when thefirst drive voltage V_(G1S) starts to decrease and the time when thedrain-source voltage V_(DS) starts to increase. However, such delay,which may result from discharging excessive charge from the first gateelectrode 21, is not shown in FIG. 13. The first conducting channel isinterrupted, and the drain-source voltage V_(DS) reaches its maximum notbefore the first drive voltage V_(G1S) falls below the first thresholdV_(TH1), which is shown at time t4 in FIG. 13. There may be a time delaybetween the time t4 when the first drive voltage V_(G1S) falls below thefirst threshold V_(TH1) and the time when the drain-source voltageV_(DS) reaches its maximum. However, such time delay is not shown inFIG. 13. At a later time t5 the first drive voltage V_(G1S) reaches thefirst off-level V_(OFF1). In the example shown in FIG. 13, the firstdrive voltage V_(G1S) decreases substantially linearly. This, however,is only an example. According to another example shown in FIG. 15, thefirst drive voltage V_(G1S) decreases non-linearly. In particular, thefirst drive voltage V_(G1S) may decrease slower as the first drivevoltage V_(G1S) approaches the first off-level V_(OFF1). According toanother example shown in FIG. 16, the first drive voltage V_(G1S)decreases in two timely subsequent non-linear sections.

Interrupting the second conducting channel includes decreasing thesecond drive voltage V_(G2S) from the second on-level V_(ON2) to thesecond off-level V_(OFF2). In the example shown in FIG. 13, the decreasebegins at time t5, which is when the first drive voltage V_(G1S) reachesthe first off-level V_(OFF1). According to another example, shown inFIG. 14, there is a delay time □t5 between the time t5 when the firstdrive voltage V_(G1S) reaches the first off-level V_(OFF1) and the timewhen the second drive voltage V_(G2S) starts to decrease.

It should be noted that although switching off the transistor device asexplained with reference to FIGS. 13 and 14 includes interrupting boththe first conducting channel and the second conducting channel, thetransistor device is already off (non-conducting) at time t4 when thefirst conducting channel is interrupted. Like in the switching-onprocedure explained before, the rate at which the drain-source voltageV_(DS) changes its voltage level is controlled by the rate at which thefirst drive voltage V_(G1S) changes its voltage level. Changing thefirst drive voltage V_(G1S), that is, discharging the first gateelectrode 21, is not associated with discharging/charging significantparasitic capacitances so that there is at most a weak Miller effectinvolved in switching off the transistor device.

FIG. 17 shows one example of a second driver stage 5 ₂ configured toswitch off the transistor device. This second driver stage 5 ₂ includesa first driver 51 ₂ configured to drive the first gate node G1, and asecond driver 52 ₂ configured to drive the second gate node G2. In thisexample, the second driver 52 ₂ includes a switch 521 ₂ connectedbetween the second gate node G2 and a supply node where a voltage havingthe second off-level V_(OFF2) is available. The first driver 51 ₂includes a series circuit with a switch 511 ₂ and a current source 512₂, wherein the series circuit with the switch 511 ₂ and the currentsource 512 ₂ is connected between the first gate node G1 and a supplynode where a supply voltage having the first off-level V_(OFF1) isavailable. According to one example, the first off-level V_(OFF1) iszero. In this case, the supply node equals the source node S. This isillustrated in dashed lines in FIG. 17.

The first driver 51 ₂ and the second driver 52 ₂ can be optimized fordifferent purposes. According to one example, the second driver 52 ₂ isoptimized to rapidly discharge the second gate electrode 31 via thesecond gate node G2. For this, the second driver 52 ₂ may be configuredto draw a high current from the second gate node G2. The first driver 51₂ may be configured to discharge the first gate electrode 21 via thefirst gate node G1 in a predefined fashion. For this, as shown in FIG.17, the first driver 51 ₂ may draw a drive current with a predefinedcurrent level from the first gate node G1. According to one example,this current level is lower than a current level of a maximum drivecurrent drawn by the second driver 52 ₂. According to one example thecurrents provided by the first and second drivers 51 ₂, 52 ₂ become zerowhen the respective drive voltage V_(G1S), V_(G2S) reaches a predefinedvoltage level. This is illustrated in FIGS. 13 and 14 in that the drivevoltages V_(G1S), V_(G2S) do not further decrease when they reach thefirst off-level V_(OFF1) and the second off-level V_(OFF2),respectively.

The second driver stage 5 ₂ shown in FIG. 17 is configured to switch offthe transistor device in accordance with the timing diagrams shown inFIG. 13 or FIG. 14. When the input signal S_(IN) indicates that it isdesired to switch off the transistor device, a control circuit 53 ₂switches on the switch 511 ₂ in the first driver 51 ₂ in order todecrease the first drive voltage V_(G1S) to the first off-levelV_(OFF1). In the first driver 51 ₂ shown in FIG. 17 the current source512 ₂ causes the first gate electrode 21 to be discharged so that thefirst drive voltage V_(G1S) decreases substantially linearly. After thefirst conducting channel has been interrupted, the control circuit 53 ₂switches on the switch 521 ₂ in the second driver 52 ₂ in order todecrease the second drive voltage V_(G2S) to the second off-levelV_(OFF2). The control circuit 53 ₂ can be configured to close the switch521 ₂ when the first drive voltage V_(G1S) has reached the firstoff-level V_(OFF1). In this case, the transistor device switches off inaccordance with the timing diagrams shown in FIG. 13. The controlcircuit 53 ₂ could also be configured to close the switch 521 ₂ after adelay time Δt5. In this case, the transistor device switches off inaccordance with the timing diagrams shown in FIG. 14. In both examples,the control circuit 53 ₂ can be configured to detect a voltage level ofthe first drive voltage V_(G1S) and start discharging the second gateelectrode 31 upon detecting or after a certain delay time Δt5 afterdetecting that the first drive voltage V_(G1S) has reached a predefinedthreshold, such as the first off-level V_(OFF1).

According to another example, the control circuit 53 ₂ discharges thefirst and second gate electrodes 21, 31, that is, drives the switches511 ₂, 521 ₂, in accordance with a predefined time scheme. For example,the control circuit 53 ₂ starts to discharge the first gate electrode 21by closing switch 511 ₂ at one time and starts to discharge the secondgate electrode 31 by closing switch 521 ₂ a fixed time periodafterwards. This time period is selected such that the second channelhas been interrupted at the time at which discharging the firstelectrode 21 starts.

FIG. 18 shows another example of the second driver stage 5 ₂. Thissecond driver stage 5 ₂ is based on the second driver stage 5 ₂ shown inFIG. 17 and is different from the second driver stage 5 ₂ shown in FIG.17 in that the first driver 51 ₂ includes a resistor 517 ₂ instead ofthe current source 512 ₂. Using this second driver stage 5 ₂ a decreaseof the first drive voltage G1 _(S) as shown in FIG. 15 can be obtained.

FIG. 19 shows another example of the second driver stage 5 ₂. Thissecond driver stage 5 ₂ is based on the second driver stage 5 ₂ shown inFIG. 17 and is different from the second driver stage 5 ₂ shown in FIG.17 in that the first driver 51 ₂ includes two series circuits eachincluding a respective switch 513 ₂, 514 ₂ and a respective resistor 515₂, 516 ₂. Both switches 513 ₂, 514 ₂ are controlled by the controlcircuit 53 ₂. A first series circuit with the switch 513 ₂ and theresistor 515 ₂ is connected between the first gate node G1 and a supplynode where an intermediate voltage V_(INT) is available. The level ofthis intermediate voltage V_(INT) is between the first on-level V_(ON),and the first off-level V_(OFF1). A second series circuit with theswitch 514 ₂ and the resistor 516 ₂ is connected between the first gatenode G1 and the supply node where a voltage with the first off-levelV_(OFF1) is available. In this second driver stage 5 ₂, the controlcircuit 53 ₂ is configured to switch on the switch 513 ₂ in the firstseries circuit when the input signal S_(IN) indicates that is desired toswitch off the transistor device. By this, the first drive voltageV_(G1S) decreases to the intermediate level V_(INT). The control circuit53 ₂ then switches off the switch 513 ₂ and switches on the switch 514 ₂in the second series circuit. By this, the voltage level of the firstdrive voltage V_(G1S) decreases to the first off-level V_(OFF1). This isin accordance with the timing diagram shown in FIG. 16.

According to another example (not shown), the first driver 51 ₂ includesa first current source instead of the resistor 515 ₂ in the first seriescircuit and a second current source instead of the resistor 516 ₂ in thesecond series circuit. In this case, the first drive voltage V_(G1S)decreases substantially linearly between the first on-level V_(ON1) andthe intermediate level V_(INT) and between the intermediate levelV_(INT) and the first off-level V_(OFF1).

According to another example (not shown), the first driver 51 ₂ includesa circuit configured to provide two different current levels. Forexample, this circuit may include two current sources or an adjustablecurrent source). By suitably timing when these current sources areactivated and deactivated the first gate electrode 21 can be dischargedin a predefined fashion.

In the examples explained above, the second driver 52 ₁, 52 ₂ in thefirst driver 5 ₁ and the second driver stage 5 ₂, respectively, is drawnto merely include a switch 521 ₁, 521 ₂ connected to the second gatenode G2. This, however, is only an example. The second driver 52 ₁, 52 ₂may additionally include a current source and/or a resistor.Nevertheless, the second driver 52 ₁, 52 ₂ is designed such that itcharges/discharges the second gate electrode 31 faster than therespective first driver 51 ₁, 51 ₂ charges/discharges the first gateelectrode 21. For example, “faster” means that a maximum absolute valueof a time derivative dV_(G1S)/dt of the first drive voltage V_(G1S) inthe charging/discharging process is lower than a maximum absolute valueof a time derivative dV_(G2S)/dt of the second drive voltage V_(G2S) inthe charging/discharging process. According to another example, “faster”means that an average charging/discharging current of the first gateelectrode 21 is lower than an average charging/discharging current ofthe second gate electrode 31.

FIG. 20 shows a drive circuit 5 according to another example. This drivecircuit includes a detection circuit 6 besides the first driver stage 5₁ and the second driver stage 5 ₂. The first driver stage 5 ₁ and thesecond driver stage 5 ₂ can be implemented in accordance with one of theexamples explained before. The detection circuit 6 is connected to thesecond gate node G2 and is configured to detect a time when the firstconducting channel has been generated or has been interrupted. That is,the detection circuit 6 is configured to detect when the first drivevoltage V_(G1S) rises above the first threshold V_(TH1) or falls belowthe first threshold V_(TH1). According to one example, the detectioncircuit 6 outputs a status signal S_(STATUS) that indicates when thefirst conducting channel has been generated or has been interrupted. Forexample, when the transistor device switches off and the detectioncircuit 6 detects that the first conducting channel has beeninterrupted, the control circuit 53 ₂ in the second driver stage 5 ₂based on the status signal S_(STATUS) may control the second driver 52 ₂to interrupt the second conducting channel as soon as the status signalS_(STATUS) indicates that the first conducting channel has beeninterrupted.

FIG. 21 shows one example of the detection circuit 6 configured todetect when the first conducting channel has been generated after thesecond conducting channel has been generated. This detection circuit 6can be activated and deactivated by a control circuit 7. The controlcircuit 7 receives the input signal S_(IN) and is further configured toactivate or deactivate the second driver 52 ₁ in the first driver stage5 ₁. Deactivating the second driver 52 ₁ may include disconnecting thesecond gate node G2 from the supply node. This is explained withreference to FIG. 22 below.

FIG. 22 shows timing diagrams of the input signal S_(IN), a drive signalS521 ₁ of the switch 521 ₁ (see, e.g., FIGS. 10-12) in the second driver52 ₁, the second drive voltage V_(GS2) and an enable signal S62 (whichmay also be referred to as activation signal) of the detection circuit6. The drive signal S521 ₁ activates or deactivates the second driver521 ₁ whereas the second driver 52 ₁ is active when the drive signalS521 ₁ switches on the switch 521 ₁ and inactive when the drive signalS521 ₁ switches off the switch 521 ₁. Just for the purpose ofillustration a signal level of the drive signal S521 ₁ that activatesthe second driver 52 ₁ is drawn as a high level in FIG. 22.Equivalently, the enable signal S62 enables or disables (activates ordeactivates) the detection circuit. Just for the purpose of illustrationa signal level of the enable signal S62 that activates the detectioncircuit is drawn as a high level in FIG. 22. The second driver 51 ₂ inthe first driver stage is activated/deactivated based on a first controlsignal S7 ₁ provided by the control circuit 7 to the first driver stage5 ₁.

Referring to the signal diagrams shown in FIG. 22, the control circuit 7is configured to activate the second driver 52 ₁ in the first driverstage 5 ₁ for an activation period T521 when the input signal S_(IN) bychanging from the off-level to the on-level indicates that it is desiredto switch on the transistor device. According to one example, a durationof the time period T521 is selected long enough for the second drivesignal V_(G2S) to reach the second on-level V_(ON2), that is, longenough for the second conducting channel to be generated, and shortenough that the transistor device is still in the off-state at the endof this time period T521 (that is, for the first conducting channel tobe interrupted). After the activation period, the control circuit 7deactivates the second driver 52 ₁ in the first driver stage 5 ₁ andactivates the detection circuit 6.

Referring to FIG. 21, the detection circuit 6 may include a voltageregulator 61 configured to regulate the second drive voltage V_(G2S)such that it remains on the second on-level V_(ON2). For this, thevoltage regulator receives the second drive voltage V_(G2S) (or a signalindicating the second drive voltage V_(G2S)) and a voltage that has thesecond on-level V_(ON2). The detection circuit 6 can beactivated/deactivated by the enable signal S62. Activating/deactivatingthe detection circuit 6 may include closing/opening a switch 62 coupledbetween an output of the voltage regulator 61 and the second gate nodeG2 and driven by the enable signal S62. It should be noted, however,that providing a switch between the output of the voltage regulator 61and the second gate node is only one of several possible means toactivate/deactivate the voltage regulator 62 by the enable signal S62;other means may be used as well.

Furthermore a current measurement and filter circuit 63 is connectedbetween the voltage regulator and the second gate node G2. The currentmeasurement and filter circuit 63 is configured to measure a currentflowing between the voltage regulator 61 and the second gate node G2 togenerate a current measurement signal and to filter this currentmeasurement signal. An output signal S63 of the current measurement andfilter circuit 63 represents the filtered current measurement signal.For example, filtering the current measurement signal includesintegrating the current measurement signal or differentiating thecurrent measurement signal. By integrating the current measurementsignal a change of an electrical charge stored in the second gateelectrode 31 can be monitored, and by differentiating the currentmeasurement signal a rapid increase or decrease of a current flowing toor from the second gate electrode 31 can be monitored. However,integrating or differentiating are only two examples of how the currentmeasurement signal can be filtered, other filter methods can be used aswell.

According to one example, the current measurement and filter circuit 63receives the enable signal S62 and is reset after the enable signal S62has disabled the detection circuit 6 and before the enable signal S62again activates the detection circuit 6. By this, the output signal S63of the current measurement and filter circuit 63 represents the currentfiltered in a time period that begins when the detection circuit 6 isenabled (activated). In this case, if filtering the current measurementincludes integrating the current measurement signal, the output signalS63 represents an amount of electrical charge provided from the voltageregulator 61 to the second gate node G2 (or received by the voltageregulator 61 from the second gate node G2) in a time period after thedetection circuit 6 has been enabled, that is, after the second gateelectrode has already been charged to the on-level V_(ON2) by the seconddriver 52 ₁ in the first driver stage 5 ₁.

An evaluation circuit 64 receives the output signal S63 of the currentmeasurement and filter circuit 63 and generates the status signalS_(STATUS) based on the output signal. According to one example, theevaluation circuit 64 generates the status signal based on comparing theoutput signal S63 with a threshold. According to one example, theevaluation circuit 64 generates a signal level of the status signalS_(STATUS) indicating that the first conducting channel has beengenerated when the output signal S63 (representing the filtered currentmeasurement signal) reaches a predefined threshold.

Why measuring the current provided by the voltage regulator to thesecond gate electrode is suitable to detect whether the first conductingchannel has been generated is explained below with reference to FIGS. 22and 23. FIG. 23 shows an equivalent circuit diagram of a double gatetransistor device. This equivalent circuit diagram shows parasiticcapacitances of the double gate transistor device and how they areconnected. Referring to FIG. 23, the double gate transistor deviceincludes a first capacitance C_(G1S) between the first gate node G1 andthe source node S1, a second capacitance C_(G1G2) between the first gatenode G1 and the second gate node G2, a third capacitance C_(G2D) betweenthe second gate node G2 and the drain node D, and a fourth capacitancebetween the drain node D and the source node S. In the following, thefirst capacitance C_(G1S) is also referred to as gate-sourcecapacitance, the second capacitance C_(G1G2) is also referred to asgate-gate capacitance, the third capacitance C_(G2D) is also referred toas gate-drain capacitance, and the fourth capacitance C_(DS) is alsoreferred to as drain-source capacitance.

The following explanation starts at the end of the time period T521.Referring to the above, at the end of this time period the second drivevoltage V_(G2S) has reached the second on-level V_(ON2), the transistordevice is still in the off-state (that is, the first drive voltageV_(G1S) is below the first threshold voltage V_(TH1)), and the detectioncircuit 6 is enabled. A voltage across the drain-source capacitanceC_(DS) may correspond to the supply voltage V+ (see, FIG. 5) at the endof the time period T521. When the first drive voltage V_(G1S) reachesthe first threshold voltage V_(TH1) the transistor device starts toconduct. At this time, the drain source capacitance C_(DS) starts to bedischarged; the electrical potential at the drain node D starts todecrease when a current through the transistor has reached its maximumcurrent level. The drain node D is capacitively coupled to the secondgate node G2 via the gate-drain capacitance C_(G2D) so that a decreasingpotential at the drain node D would decrease the electrical potential atthe second gate node G2 unless this electrical potential at the secondgate node G2 is tied to a fixed potential (such as in the examples shownin FIGS. 10-12, where the second gate node G2 is tied to V_(ON2)) orregulated. In the detection circuit 6 shown in FIG. 21, after the timeperiod T521, the voltage regulator 61 regulates the electrical potentialat the second gate node G2 such that the drive voltage V_(G2S)substantially remains at V_(ON2). This regulation requires dischargingthe gate-drain capacitance C_(G2D) after the transistor device switcheson, whereas discharging the gate-drain capacitance C_(G2D) requires thevoltage regulator 61 to drive a current I6 into the second gate node G2.

This is illustrated in FIG. 24, where signal diagrams of the inputsignal S_(IN), the second drive voltage V_(GS2), the first drive signalV_(GS1), the current I6 from the voltage regulator to the second gatenode G2, the measurement and filter signal S63, and the status signalS_(STATUS) are shown. For the purpose of explanation it is assumed thatthe current I6 starts to flow when the first drive voltage V_(GS1)reaches the first threshold V_(TH1). The current measurement and filtercircuit 63 measures the current I6 to generate a current measurementsignal and filter this current measurement signal.

According to one example, filtering the current measurement signalincludes integrating the current measurement signal, so that themeasurement and filter signal S63 represents a change of the chargingstate of the gate drain capacitance C_(G2D). According to one example,the measurement and filter signal S63 is proportional to an integral ofthe current I6. It can be assumed that the transistor device has changedits operation state when a certain amount of charge has been provided tothe second gate electrode 31, that is, when the measurement and filtersignal S63 has reached a predefined threshold S63 _(TH) so that theevaluation circuit 64 changes a signal level of the status signalS_(STATUS) (asserts the status signal S_(STATUS)) to indicate that thetransistor device has switched on when the measurement and filter signalS63 has reached the predefined threshold S63 _(TH).

According to one example, the detection circuit 6 is not only configuredto detect when the transistor device switches from the off-state to theon-state (when the first conducting channel has been generated after thesecond conducting channel has been generated), but may also detect whenthe transistor device switches from the on-state to the off-state (whenthe first conducting channel has been interrupted before the secondconducting channel is interrupted). Referring to the above, when thedevice switches on, the second gate electrode 31 changes its chargingstate when the first conducting channel is generated. This change of thecharging state is associated with a charging current that can bemonitored by the measurement and filter circuit. When the transistordevice switches off by first interrupting the first conducting channeland then interrupting the second conducting channel, as explained withreference to FIGS. 13 and 14, the change of the charging state of thesecond gate electrode is reversed. That is, a current flows from thesecond gate electrode 31 and the second gate node G2, respectively, tothe voltage regulator and can be measured by the measurement and filtercircuit 63. According to one example, the detection circuit 6 staysactivated throughout the on-state of the transistor device and theevaluation circuit 64 sets the status signal S_(STATUS) to a signallevel indicating that the first conducting channel has been interruptedwhen the output signal S63 of the measurement and filter circuit fallsbelow the predefined threshold. This is illustrated in FIG. 25 wheresignal diagrams of the same signals as in FIG. 24 are shown duringswitching off.

According to another example (not shown), the measurement and filtercircuit 63 is reset after the status signal S_(STATUS) has indicatedthat the transistor device has been switched on so that the measurementand filter signal S63 becomes zero. In this case, the measurement andfilter signal S63 is compared with a second threshold during turn-off,and the status signal S_(STATUS) is set back to the signal levelindicating that the transistor device has been switched off when themeasurement and filter signal S63 falls below the second threshold.

According to one example, the first gate electrode 21 is driven based onthe status signal. For this, at least one of the first driver stage 5 ₁and the second driver stage 5 ₂ receives the status signal S_(STATUS).According to one example, a time scheme of driving the first gateelectrode 21 is dependent on the status signal S_(STATUS). For example,if the first gate electrode 21 is driven in accordance with the drivescheme shown in FIG. 9 where the drive current changes from a firstcurrent level (defined by current source 515 ₁ shown in FIG. 12) to asecond current level (defined by current source 516 ₁ shown in FIG. 12)the time of changing the current level can be dependent on the statussignal. That is, the first gate electrode 21 may be driven (charged)based on the first current level until the status signal S_(STATUS)indicates that the first conducting channel has been generated, andbased on the second current level afterwards. Equivalently, when thetransistor device switches off the first gate electrode may be driven(discharged) based on a first current level until the status signalS_(STATUS) indicates that the first conducting channel has beeninterrupted, and based on a second current level afterwards. It shouldbe noted that the first current level when driving the first gateelectrode 21 to generate the first conducting channel can be differentfrom the first current level when driving the first gate electrode 21 tointerrupt the first conducting channel, and the second current levelwhen driving the first gate electrode 21 to generate the firstconducting channel can be different from the second current level whendriving the first gate electrode 21 to interrupt the first conductingchannel. In general, the first gate electrode can be driven based on afirst drive parameter until the status signal S_(STATUS) indicates thatan operation state of the transistor device has changed, and based on asecond drive parameter afterwards.

The operation state of the transistor device changes each time the firstconducting channel is either generated or interrupted. In the exampleexplained above, the first drive parameter is a first current level ofthe drive current, and a second drive parameter is a second currentlevel of the drive current. However, the first and second driveparameters are not restricted to be current levels. According to anotherexample, the first and second drive parameters include a resistancecoupled to the first gate node G1, so that a first resistance can beconnected between the first gate node G1 and a supply node until thestatus signal S_(STATUS) indicates that the operation status has changedand a second resistance can be connected between the first gate node G1and a supply node after the status signal S_(STATUS) has indicatedindicates that the operation status has changed. According to yetanother example, the supply potential applied to the first gateelectrode G1 may change based on the status signal S_(STATUS). The firstand second drive parameters could even be combinations of the above. Forexample, a first supply potential may be applied to the first gate nodeG1 via a first resistor (such as V_(INT) via resistor 515 ₂ in the firstdrive circuit 51 ₂ shown in FIG. 19), and first second potential may beapplied to the first gate node G1 via a second resistor (such asV_(OFF1) via resistor 516 ₂ in the first drive circuit 51 ₂ shown inFIG. 19).

According to another example, the detection circuit 6 is used todiagnose the transistor device before it is switched on. Referring tothe above, the first gate electrode 21 and the second gate electrode 31are capacitively coupled. Thus, if the transistor device has beenproperly connected in an application circuit, such as an applicationcircuit illustrated in FIG. 5, and the transistor device is faultlesschanging the electrical potential at the first gate node G1 is supposedto either change the electrical potential at the second gate node G2 orcause a capacitive displacement current to flow from or into the secondgate node. The electrical potential of the second gate node G2 changesif the second gate node G2 is floating during the diagnosis, that is,not clamped to a fixed potential. A capacitive displacement currentflows if the electrical potential at the second node is clamped to afixed potential, such as the second off-level, during the diagnosis.Thus, diagnosing the device may include changing the electricalpotential at the first gate node G1, for example, from the firstoff-level V_(OFF1) to the first on-level V_(ON1) and monitoring thesecond gate node G2. According to one example, the transistor device isconsidered to be faultless and properly connected if the electricalpotential at the second gate node G2 changes or a capacitivedisplacement current is detected. Additionally or alternatively,diagnosing the transistor device may include changing the electricalpotential at the second gate node G2 and monitoring the first gate nodeG1.

During the diagnosis the transistor device is in the off-state so thatpotential faults can be detected before the transistor device isswitched on for the first time.

In the examples explained above the transistor device is a field-effectcontrolled transistor device, in particular an MOS transistor, such as aMOSFET or an IGBT. The method explained above for driving a transistordevice with two gate electrodes and two gate nodes G1, G2, however, isnot restricted to this specific type of transistor device, but may beused for driving any other type of transistor device such as, forexample, a HEMT or a GIT as well. Just for the purpose of illustration acircuit symbol of a HEMT with two gate electrodes G1, G2 is shown inFIG. 26. Like in each of the transistor devices explained before, afirst drive voltage V_(G1S) of the HEMT is a voltage between a firstgate node G1 and a source node and a second drive voltage V_(G1S) of theHEMT is a voltage between a second gate node G2 and the source node S.The same applies to a GIT.

Driving a HEMT or GIT in accordance with the method explained aboveincludes one of switching on and off the HEMT or GIT. Switching onincludes generating a first conducting channel by driving a first gateelectrode coupled to the first gate node and, before generating thefirst conducting channel, generating a second conducting channel bydriving a second gate electrode coupled to the second gate node. Thesecond conducting channel may be switched on faster than the firstconducting channel. Switching off includes interrupting a firstconducting channel by driving a first gate electrode and, afterinterrupting the first conducting channel, interrupting a secondconducting channel by driving a second gate electrode. The secondconducting channel may be interrupted faster than the first conductingchannel. The voltage levels of the first and second drive voltagesV_(G1S), V_(G2S) required to generate or interrupt the first and secondconducting channels are dependent on the specific type of HEMT or GIT.Some examples are explained below.

FIG. 27 shows a vertical sectional view of a HEMT according to oneexample. The HEMT includes a semiconductor body 200 with a firstsemiconductor layer 210 and a second semiconductor layer 220 adjoiningthe first semiconductor layer 210. According to one example, the firstsemiconductor layer 210 includes a group III nitride of a first type,and the second semiconductor layer 220 includes a group III nitride of asecond type different from the first type. The first and second typegroup III nitrides are chosen such that there is a two-dimensionalelectron gas (2DEG) in at least one of the first and secondsemiconductor layers 210, 220 in a region close to an interface betweenthe first and second semiconductor layers 210, 220. Referring to FIG.27, a source electrode 213 is connected to the first semiconductor layer210 and the second semiconductor layer 220. This source electrode 213 isconnected to a source node S or forms a source node S of the transistordevice. A drain electrode 214 is connected to a drain node D or forms adrain node D of the transistor device. The drain electrode 214 iselectrically connected to the first semiconductor layer 210 and thesecond semiconductor layer 220 and is spaced apart from the sourceelectrode 213 in a current flow direction of the transistor device. Inthe example shown in FIG. 27, the current flow direction is a directionparallel to the 2DEG. In the example shown in FIG. 27, this direction isa lateral (horizontal) direction of the semiconductor body 200.

Referring to FIG. 27, the transistor device further includes a firstgate electrode 221 and a second gate electrode 231. These first andsecond gate electrodes 221, 231 are spaced apart from each other in thecurrent flow direction of the transistor device, wherein the first gateelectrode 221 is closer to the source electrode 213 than the second gateelectrode 231. The second gate electrode 231 is closer to the drainelectrode 214 than the first gate electrode 221. According to oneexample, as shown in FIG. 207, a distance between the first gateelectrode 221 and the source electrode 213 is shorter than the distancebetween the second gate electrode 231 and the drain electrode 214.According to one example, a distance between the second gate electrode231 and the drain electrode 214 is more than three times, more than fivetimes, or more than ten times a distance between the first gateelectrode 221 and the source electrode 213. In the example shown in FIG.27, the transistor device further includes a third semiconductor layer230 of a group III nitride. The semiconductor layer 230 adjoins thesecond semiconductor layer 220 and separates the first gate electrode221 and the second gate electrode 231 from the second semiconductorlayer 220, wherein both the first gate electrode 221 and the second gateelectrode 231 adjoin the third semiconductor layer 230 o. Optionally, apassivation layer 240 covers those regions of the third semiconductorlayer 230 that are not covered by the first gate electrode 221 and thesecond gate electrode 231. Optionally, a field electrode 225 adjoins thesecond gate electrode 231 but does not adjoin the third semiconductorlayer 230 o. That is, the field electrode 225 is spaced apart from thethird semiconductor layer 230.

According to one example, the first type group III nitride of the firstsemiconductor layer 210 is gallium nitride (GaN), and the second typegroup III nitride of the second semiconductor layer 220 is a galliumalloy nitride such as, for example, aluminum gallium nitride (AlGaN),indium gallium nitride (InGaN), aluminum indium gallium nitride(AlInGaN), or the like. According to one example, the thirdsemiconductor layer 230 includes the first type group III nitride. Eachof the first gate electrode 221, the second gate electrode 231, thesource electrode 213, the drain electrode 214, and the optionally fieldelectrode 225 includes an electrically conducting material which mayinclude one or more of polycrystalline silicon, a metal silicide, metalslike e.g. aluminum, copper, nickel, titanium, tantalum, gold, conductiveceramics like e.g. titanium nitride or the like. According to oneexample, materials of the source electrode 213 and the drain electrode214 are chosen such that there is an ohmic contact between the sourceelectrode 213 and each of the first semiconductor layer 210 and thesecond semiconductor layer 220 and that there is an ohmic contactbetween the drain electrode 214 and each of the first semiconductorlayer 210 and the second semiconductor layer 220.

According to one example the first layer 210 and the third layer 230 arep-doped semiconductor layers. A doping concentration is, for example,higher than 1E15 cm⁻³, higher than 1E17 cm⁻³, or even higher than 1E19cm⁻³. According to one example, the first and second layers 210, 230 areGaN layers doped with magnesium (Mg). The third layer is an AlGaN layer,for example, in which the dopant is aluminum (Al). These layers 210,220, 230 may be formed and doped by epitaxial growth processes.

The HEMT device shown in FIG. 27 is a normally-on device. That is, thetransistor device is an on-state when each of the first drive voltageV_(G1S), V_(G2S) is zero. In the on-state, the 2DEG forms a conductingchannel between the source electrode 213 and the drain electrode 214.

The HEMT device shown in FIG. 27 can be switched off by generating thefirst and second drive voltages V_(G1S), V_(G2S) in accordance with oneof the timing diagrams shown in FIGS. 13 and 14, for example. The firston-level V_(ON1) and the second on-level V_(ON2) are zero or positivevoltage levels, while each of the first off-level V_(OFF1), V_(OFF2) isa negative voltage level. According to one example, each of the firstoff-level and the second off-level is selected from a range of between−1V and −3V. Like in the examples explained before, the first on-levelV_(ON1) and the second on-level V_(ON2) can be substantially equal orcan be different from each other. Likewise, the first off-level V_(OFF1)and the second off-level V_(OFF2) can be substantially equal or can bedifferent from each other. In the off-state, the first gate electrode221 interrupts a first conducting channel, which is a section of the2DEG below the first gate electrode 221, and the second gate electrode231 interrupts a second conducting channel, which is a section of the2DEG below the second gate electrode 231. When the transistor device isin the off-state it can be switched on by generating the first drivevoltage V_(G1S), V_(G2S) in accordance with one of the timing diagramsshown in FIGS. 6 to 9.

An alternative method for switching on the HEMT device shown in FIG. 27is illustrated in FIG. 28, and an alternative method for switching offthe HEMT device shown in FIG. 27 is illustrated in FIG. 29. Each ofthese Figures shows timing diagrams of the input signal S_(IN), thefirst and second drive voltages V_(G1S), V_(G2S), and the drain-sourcevoltage V_(DS). The methods illustrated in FIGS. 28 and 29 are differentfrom the methods explained before in that the second drive voltageV_(G2S) is zero throughout the different operation states of thetransistor device. This can be obtained, for example, by electricallyconnecting the second gate node G2 with the source node S. In thisexample, the operation state of the HEMT device is only controlled bythe first drive voltage V_(G1S). When, for example, a positive voltageis applied between the drain node D and the source node S and the firstgate electrode 221 is driven such that it interrupts the 2DEG anelectrical potential in the first and second semiconductor layers 210,220 increases beginning at the source electrode 213, wherein thisincreasing electrical potential (in connection with the electricalpotential of the second gate electrode 231 being clamped to theelectrical potential of the source electrode 213) also causes the 2DEGbelow the second gate electrode 231 to be interrupted. In this way, thefirst conducting channel below the first gate electrode 221 and thesecond conducting channel below the second gate electrode 231 areinterrupted.

FIG. 30 shows one example of a normally-off HEMT. In this example, thefirst gate electrode 221 extends through the second semiconductor layer220 into the first semiconductor layer 210 and is dielectricallyinsulated from these semiconductor layers 210, 220 by a gate dielectric222. Equivalently, the second gate electrode 231 extends through thesecond semiconductor layer 220 into the first semiconductor layer 210and is dielectrically insulated from these semiconductor layers 220, 210by a second gate dielectric 232. In this transistor device there is a2DEG between the first gate electrode 221 and the source electrode 213,between the two gate electrodes 221, 231 and between the second gateelectrode 231 and the drain electrode 214. The 2DEG, however, isinterrupted by the two gate electrodes 221, 231. The transistor deviceis in the on-state when drive voltages V_(G1S), V_(G2S) are applied tothe first and second gate nodes G1, G2 such that conducting channels aregenerated in the first semiconductor layer 210 along the first andsecond gate dielectrics 222, 232. The normally off-HEMT shown in FIG. 30can be switched on and off in the same way as any of the normally-offdevices explained herein before. According to one example, each of thefirst on-level V_(ON1) and the second on-level V_(ON2) is a positivelevel, and each of the first off-level V_(OFF1) and the second off-levelV_(ON1), V_(ON2) is zero or a negative level. According to one example,each of the first and second on-levels is selected from a range ofbetween 3V and 10V. The conducting channels generated by the gateelectrodes 221, 231 when a suitable drive potential is applied areinversion channels, for example.

FIG. 31 shows a combination of the transistor devices shown in FIGS. 27and 30. In this example, the first gate electrode 221 is of the sametype as the first gate electrode 221 shown in FIG. 30 and the secondgate electrode 231 is of the same type as the second gate electrode 231explained with reference to FIG. 27. In this example, the on-levelV_(ON1) and off-level V_(OFF1) of the first drive voltage V_(G1S) may beas explained in context with the first gate electrode 221 in the deviceshown in FIG. 30, and the on-level V_(ON2) and off-level V_(OFF2) of thesecond drive voltage V_(G2S) may be as explained in context with thesecond gate electrode 231 in the device shown in FIG. 30.

FIG. 32 shows a vertical cross-sectional view of a GIT device accordingto one example. This transistor device is different from the HEMT deviceexplained before in that the first semiconductor layer 210 and thesecond semiconductor layer 220 are intrinsic layers. According to oneexample, “intrinsic” means that a doping concentration is less than 1E14cm⁻³, less than 1E13 cm⁻³, or even less than 1E12 cm⁻³. The thirdsemiconductor layer includes two sections, a first section 2301 betweenthe first gate electrode 221 and the second semiconductor layer 220, andthe second section 230 ₂ between the second gate electrode 231 and thesecond semiconductor layer 220. These layer sections 230 ₁, 230 ₂ aredoped semiconductor layers. According to one example, these layersections 230 ₁, 230 ₂ are p-doped. According to one example, a dopingconcentration of these layer sections is higher than 1E14 cm⁻³, higherthan 1E16 cm⁻³, or even higher than 1E18 cm⁻³. Everything else that hasbeen explained with reference to the first, second and thirdsemiconductor layers 210, 220, 230 above applies to the first, secondand third semiconductor layers shown in FIG. 32 equivalently. The GITdevice shown in FIG. 32 is a normally-off device. In this type of devicethere is a 2DEG between the first semiconductor layer 210 and the secondsemiconductor layer 220, wherein the doped layer sections 230 ₁, 230 ₂below the gate electrodes 221, 231 cause the 2DEG to be depleted belowthe layer sections 230 ₁, 230 ₂ when the drive voltages are zero orbelow. A 2DEG is generated below the respective layer section when adrive voltage (gate-source voltage) is applied to the respective gatenode G1, G2 such that charge carriers (holes) are injected by the layersections 230 ₁, 230 ₂ into the second layer 220. These charge carriersin the second layer 220 cause further charge carriers (electrons) in thefirst layer 210 to move to the interface between the first and secondlayer 210, 220 and form a 2DEG. This device can be switched on an off inthe same way as any of the normally-off devices explained herein before.According to one example, the on-levels V_(ON1), V_(ON2) are selectedfrom a range of between 0.5V and 10V, in particular between +2V and +5V,and the off-levels V_(OFF1), V_(OFF2) are selected from a range ofbetween −15V and 0V, in particular between −10V and −2V.

In the examples explained above, drive signals applied to the first andsecond gate node G1, G2 in order to switch on or off the transistordevice are drive voltages, such as gate-source voltages. However, thereare types of transistor devices, such as the GIT, that can also beswitched on or off dependent on a current driven into the respectivegate node G1, G2. Thus, in particular in a GIT, the drive signal may bea drive current as well or, as a further alternative, may be a drivecurrent for turning-on the device and drive voltage for turning-off thedevice. Everything that has been explained before with regard to drivinga transistor device based on drive voltages applies to driving atransistor device, such as a GIT, based on a drive current as well. Inparticular, timing diagrams of drive currents may correspond to thetiming diagrams of drive voltages explained before. That is, whenswitching on, for example, a drive current driven into the second gatenode G2 may increase more rapidly (before the current driven into thefirst gate node G1 increases) than a drive current driven into the firstgate node G1. And, when switching off, the drive current driven into thesecond gate node G2 may decrease more rapidly (after the current driveninto the first gate node G1) than the drive current driven into thefirst gate node G1.

FIG. 33 shows a combination of the transistor devices shown in FIGS. 27and 32. In this example, the first gate electrode 221 is of the sametype as the first gate electrode 221 shown in FIG. 32. This type of gateelectrode may be referred to as GIT gate. The second gate electrode 231adjoins the second semiconductor layer 220 in this example and may bereferred to as HEMT gate. In this example, the first gate 221 inconnection with the first layer 230 ₁ generates a 2DEG at the interfacebetween the first and second layers 210, 220 below the first gateelectrode 221 when a drive signal with an on-level is applied, whereinan on-level is one of the on-levels explained with reference to FIG. 32,for example. The second gate 231 in connection with the second layer 230₂ generates a 2DEG at the interface between the first and second layers210, 220 below the second gate electrode when a drive signal with anon-level is applied, wherein an on-level is one of the on-levelsexplained with reference to FIG. 27, for example.

FIG. 34 shows one example of how connection lines between the driver andthe gate and source nodes S, G1, G2 may be arranged in order to largelyavoid magnetic or capacitive crosstalk. These lines are referred to asgate and source lines in the following. In this example, each of thegate lines crosses the source line several times in different layers.Just for the purpose of illustration it may be assumed that thosesections of the zig-zag gate lines that are drawn in solid lines crossthe source line in a first layer above the source line and that thosesections of the zig-zag gate lines that are drawn in dashed lines crossthe source lines in a second layer below the source line. The sourceline may also be zig-zag-shaped (not shown in FIG. 34). In this example,each of the gate lines alternatingly crosses the source line in thefirst layer and the second layer. The layer sections of one gate linemay be connected by connectors, such as vias. These connectors, whichextend in a direction perpendicular to the drawing plane shown in FIG.34, are not shown. In each case, the gate lines and the source line areinsulated from each other.

Examples of methods explained before relate to switching on or switchingoff a transistor device. Switching on may include generating a firstconducting channel by driving a first gate electrode and, beforegenerating the first conducting channel, generating a second conductingchannel by driving a second gate electrode. Switching off may includeinterrupting a first conducting channel by driving a first gateelectrode and, after interrupting the first conducting channel,interrupting a second conducting channel by driving a second gateelectrode. Referring to the above, generating the first conductingchannel may include generating an on-level of a first drive signal(e.g., a drive voltage) applied to the first gate electrode, andinterrupting the conducting channel may include generating an off-levelof the first drive signal. Equivalently generating the second conductingchannel may include generating an on-level of a second drive signal(e.g., a drive voltage) applied to the second gate electrode, andinterrupting the conducting channel may include generating an off-levelof the second drive signal. The on-level and the off-level are dependenton the specific type of transistor device.

The following examples may illustrate one or more aspects of thedisclosure.

Example 1

A method including: switching on a transistor device by generating afirst conducting channel by driving a first gate electrode and, beforegenerating the first conducting channel, generating a second conductingchannel by driving a second gate electrode, wherein the second gateelectrode is adjacent the first gate electrode in a current flowdirection of the transistor device.

Example 2

The method of example 1, wherein the transistor device is a field-effectcontrolled transistor device, wherein generating the first conductingchannel includes generating the first conducting channel in a bodyregion, wherein generating the second conducting channel includesgenerating the second conducting channel in the body region, wherein thefirst gate electrode is dielectrically insulated from the body region bya first gate dielectric, wherein the second gate electrode isdielectrically insulated from the body region by a second gatedielectric, wherein the second gate electrode is separated from thefirst gate electrode by a separation layer, and wherein the body regionis arranged between a source region and a drift region, and wherein thedrift region is arranged between body region and a drain region.

Example 3

The method of example 1, wherein the transistor device is a HEMT device.

Example 4

The method of example 3, wherein the HEMT device is a normally-on HEMTdevice.

Example 5

The method of example 3, wherein the HEMT device is a normally-off HEMTdevice.

Example 6

The method of example 1, wherein the transistor device is a GIT device.

Example 7

The method of example 6, wherein the GIT device includes a firstinjection gate adjoining the first gate electrode and a second injectiongate adjoining the second gate electrode.

Example 8

The method of example 6, wherein the GIT device includes only oneinjection gate.

Example 9

The method of example 1, wherein driving the first gate electrodeincludes increasing a first drive signal, and wherein driving the secondgate electrode includes increasing a second drive signal from a secondoff-level to a second on-level.

Example 10

The method of example 9, wherein driving the first gate electrodeincludes clamping the second gate electrode to the second on-level.

Example 11

The method of example 9, wherein the second off-level is different fromthe first off-level.

Example 12

The method of example 9, wherein driving the first gate electrode andthe second gate electrode includes increasing the second drive signalfaster than the first drive signal.

Example 13

The method of example 1, further including: detecting a change in anoperation state of the transistor device, wherein detecting theoperation state includes monitoring at least one electrical parameter ofthe second gate electrode.

Example 14

The method of example 13, wherein monitoring the at least one electricalparameter of the second gate electrode includes monitoring at least oneof an electrical potential and a current to or from the second gateelectrode.

Example 15

The method of example 14, wherein monitoring the at least one electricalparameter includes: filtering a signal representing a current to or fromthe second gate electrode to generate a filter signal; and comparing thefilter signal with a threshold.

Example 16

The method of example 13, wherein detecting the change of the operationstate includes detecting the change in the operation state if the filtersignal reaches the threshold.

Example 17

The method of example 13, wherein driving the first gate electrodefurther includes driving the first gate electrode based on a detectedchange of the operation state.

Example 18

The method of example 17, wherein driving the first gate electrode basedon a detected change of the operation state includes: driving the firstgate electrode in accordance with a first drive parameter before thechange of the operation state has been detected; and driving the firstgate electrode in accordance with a second drive parameter differentfrom the first drive parameter after the change of the operation statehas been detected.

Example 19

The method of example 18, wherein the first drive parameter includes afirst current level of a drive current into the first gate electrode andthe second drive parameter includes a second current level of the drivecurrent higher than the first current level.

Example 20

A method including: switching off a transistor device by interrupting afirst conducting channel by driving a first gate electrode and, afterinterrupting the first conducting channel, interrupting a secondconducting channel by driving a second gate electrode, wherein thesecond gate electrode is arranged adjacent the first gate electrode in acurrent flow direction of the transistor device.

Example 21

The method of example 20, wherein the transistor device is afield-effect controlled transistor device, wherein interrupting thefirst conducting channel includes interrupting the first conductingchannel in a body region, wherein interrupting the second conductingchannel includes interrupting the second conducting channel in the bodyregion, wherein the first gate electrode is dielectrically insulatedfrom the body region by a first gate dielectric, wherein the second gateelectrode is dielectrically insulated from the body region by a secondgate dielectric, wherein the second gate electrode is separated from thefirst gate electrode by a separation layer, and wherein the body regionis arranged between a source region and a drift region, and wherein thedrift region is arranged between body region and a drain region.

Example 22

The method of example 20, wherein the transistor device is a HEMTdevice.

Example 23

The method of example 22, wherein the HEMT device is a normally-on HEMTdevice.

Example 24

The method of example 22, wherein the HEMT device is a normally-off HEMTdevice.

Example 25

The method of example 20, wherein the transistor device is a GIT device.

Example 26

The method of example 25, wherein the GIT device includes a firstinjection gate adjoining the first gate electrode and a second injectiongate adjoining the second gate electrode.

Example 27

The method of example 25, wherein the GIT device includes only oneinjection gate.

Example 28

The method of example 20, wherein driving the first gate electrodeincludes decreasing a first drive signal from a first on-level to afirst off-level, and wherein driving the second gate electrode includesdecreasing a second drive signal between the second gate electrode andthe source region from a second on-level to a second off-level.

Example 29

The method of example 28, wherein driving the first gate electrodeincludes clamping the second gate electrode to the second on-level.

Example 30

The method of example 28, wherein the second off-level is different fromthe first off-level.

Example 31

The method of example 28, wherein driving the first gate electrode andthe second gate electrode includes decreasing the second drive signalfaster than the first drive signal.

Example 32

The method of example 20, further including: detecting a change in anoperation state of the transistor device, wherein detecting theoperation state includes monitoring at least one electrical parameter ofthe second gate electrode.

Example 33

The method of example 32, wherein monitoring the at least one electricalparameter of the second gate electrode includes monitoring at least oneof an electrical potential and a current to or from the second gateelectrode.

Example 34

The method of example 33, wherein monitoring the at least one electricalparameter includes: filtering a signal representing a current to or fromthe second gate electrode to obtain a filter signal; and comparing thefilter signal with a threshold.

Example 35

The method of example 34, wherein detecting the change of the operationstate includes detecting the change in the operation state if the filtersignal reaches a threshold.

Example 36

The method of example 32, wherein driving the first gate electrodefurther includes driving the first gate electrode based on a detectedchange of the operation state.

Example 37

The method of example 36, wherein driving the first gate electrode basedon a detected change of the operation state includes: driving the firstgate electrode in accordance with a first drive parameter before thechange of the operation state has been detected; and driving the firstgate electrode in accordance with a second drive parameter differentfrom the first drive parameter after the change of the operation statehas been detected.

Example 38

The method of example 37, wherein the first drive parameter includes afirst current level of a drive current into the first gate electrode andthe second drive parameter includes a second current level of the drivecurrent higher than the first current level.

Example 39

A method, including: driving a first gate electrode of a transistordevice and monitoring at least one electrical parameter of a second gateelectrode of the transistor device.

Example 40

The method of example 39, wherein the transistor device is afield-effect controlled transistor device, wherein the first gateelectrode is dielectrically insulated from a body region by a first gatedielectric, wherein the second gate electrode is dielectricallyinsulated from the body region by a second gate dielectric, arrangedadjacent the first gate electrode, and separated from the first gateelectrode by a separation layer, and wherein the body region is arrangedbetween a source region and a drift region, and wherein the drift regionis arranged between body region and a drain region.

Example 41

The method of example 39, wherein the transistor device is one of a HEMTdevice and a GIT device.

Example 42

The method of example 39, wherein monitoring the at least one electricalparameter of the second gate electrode includes monitoring at least oneof an electrical potential and a current to or from the second gateelectrode.

Example 43

A transistor device comprising at least one transistor cell, wherein theat least one transistor cell includes: a drift region, a body region, asource region and a drain region, wherein the body region is arrangedbetween the source region and the drift region, and wherein the driftregion is arranged between body region and the drain region; a firstgate electrode dielectrically insulated from the body region by a firstgate dielectric; and a second gate electrode, wherein the second gateelectrode is dielectrically insulated from the body region by a secondgate dielectric, arranged adjacent the first gate electrode, andseparated from the first gate electrode by a separation layer.

Example 44

The transistor device of example 43, wherein the separation layerincludes a dielectric layer.

Example 45

The transistor device of example 43, comprising a plurality oftransistor cells, wherein each of the plurality of transistor cells hasits respective source region connected to a source node common to theplurality of transistor cells, wherein each of the plurality oftransistor cells has its respective first gate electrode connected to afirst gate node common to the plurality of transistor cells, and whereineach of the plurality of transistor cells has its respective second gateelectrode connected to a second gate node common to the plurality oftransistor cells.

Example 46

The transistor device of example 43, wherein the drain region has adoping concentration higher than a doping concentration of the driftregion.

Example 47

The transistor device of example 46, wherein a doping concentration ofthe drain region is at least 1E3 times or 1E4 times a dopingconcentration of the drift region.

Example 48

The transistor device of example 46, wherein a doping type of the drainregion equals a doping type of the drift region.

Example 49

The transistor device of example 46, wherein a doping type of the drainregion is complementary to a doping type of the drift region.

Example 50

The transistor device of example 43, wherein a doping concentration ofthe body region is such that an integral of the doping concentration ofthe body region along a path that begins at a junction between the driftregion and a body region and extends along the second gate electrode ishigher than a breakthrough charge of a semiconductor material of thebody region.

Example 51

The transistor device of example 43, wherein the transistor deviceincludes a current flow direction, and wherein the second gate electrodeis adjacent the first gate electrode in the current flow direction.

Example 52

A transistor device, including: a semiconductor body with a firstsemiconductor layer comprising a first type of group III nitride and asecond semiconductor layer adjoining the first semiconductor layer andcomprising a second type group III nitride; a source electrode connectedto the first semiconductor layer and the second semiconductor layer; adrain electrode spaced apart from the source electrode and connected tothe first semiconductor layer and the second semiconductor layer; and afirst gate electrode and a second gate electrode that are spaced apartin a current flow direction of the transistor device.

Example 53

The transistor device of example 52, wherein the semiconductor bodyfurther includes a third semiconductor layer adjoining the secondsemiconductor layer and comprising a group III nitride, and wherein atleast one of the first gate electrode and the second gate electrodeadjoins the third semiconductor layer and is separated from the secondsemiconductor layer by the third semiconductor layer.

Example 54

The transistor device of example 52, wherein at least one of the firstgate electrode and the second gate electrode extends through the secondsemiconductor layer into the first semiconductor layer and isdielectrically insulated from the second semiconductor layer and thefirst semiconductor layer by a gate dielectric.

Example 55

The transistor device of example 52, wherein each of the firstsemiconductor layer and the second semiconductor layer is a dopedsemiconductor layer.

Example 56

The transistor device of example 52, wherein each of the firstsemiconductor layer and the second semiconductor layer is an intrinsicsemiconductor layer.

Example 57

The transistor device of example 56, wherein the semiconductor bodyfurther includes at least one third semiconductor layer adjoining thesecond semiconductor layer and comprising a doped group III nitride, andwherein at least one of the first gate electrode and the second gateelectrode adjoins the at least one third semiconductor layer and isseparated from the second semiconductor layer by the third semiconductorlayer.

Example 58

The transistor device of example 57, wherein the first gate electrodeadjoins the at least one third semiconductor layer, and wherein thesecond gate electrode adjoins the second semiconductor layer.

Example 59

The transistor device of example 52, further including: a fieldelectrode adjoining the second gate electrode.

Example 60

The transistor device of example 52, wherein the second gate electrodeis electrically connected with the source electrode.

Example 61

The transistor device of example 52, wherein the first type of group IIInitride includes gallium nitride (GaN), and wherein the second type ofgroup III nitride includes aluminum gallium nitride (AlGaN).

Example 62

A drive circuit, including: an input configured to receive an inputsignal; a first output configured to be coupled to a first gate node ofa transistor device; and a second output configured to be coupled to asecond gate node of a transistor device, wherein the drive circuit isconfigured to drive the first gate node and the second gate node basedon the input signal, wherein the drive circuit is configured to detectan operation state of the transistor device based on monitoring at leastone electrical parameter at the second output.

Example 63

The drive circuit according to example 62, wherein the drive circuit isconfigured to adjust a time scheme of driving the first gate node basedon detecting the operation state.

Example 64

A drive circuit, comprising: an input configured to receive an inputsignal; a first output configured to be coupled to a first gate node ofa transistor device; and a second output configured to be coupled to asecond gate node of a transistor device; and wherein the drive circuitis configured to operate in a diagnostic mode, wherein in the diagnosticmode, the transistor device is configured to diagnose the transistordevice based on driving the first gate node via the first output andmonitoring at least one electrical parameter at the second output.

Example 65

The drive circuit of example 64, wherein the drive circuit is furtherconfigured to operate in a drive mode, wherein in the drive mode thedrive circuit is configured to drive the first gate node and the secondgate node based on the input signal.

Although various exemplary embodiments of the invention have beendisclosed, it will be apparent to those skilled in the art that variouschanges and modifications can be made which will achieve some of theadvantages of the invention without departing from the spirit and scopeof the invention. It will be obvious to those reasonably skilled in theart that other components performing the same functions may be suitablysubstituted. It should be mentioned that features explained withreference to a specific figure may be combined with features of otherfigures, even in those cases in which this has not explicitly beenmentioned. Further, the methods of the invention may be achieved ineither all software implementations, using the appropriate processorinstructions, or in hybrid implementations that utilize a combination ofhardware logic and software logic to achieve the same results. Suchmodifications to the inventive concept are intended to be covered by theappended claims.

Spatially relative terms such as “under,” “below,” “lower,” “over,”“upper” and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first,” “second” and the like, are also used to describevarious elements, regions, sections, etc. and are also not intended tobe limiting. Like terms refer to like elements throughout thedescription.

As used herein, the terms “having,” “containing,” “including,”“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a,” “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

With the above range of variations and applications in mind, it shouldbe understood that the present invention is not limited by the foregoingdescription, nor is it limited by the accompanying drawings. Instead,the present invention is limited only by the following claims and theirlegal equivalents.

What is claimed is:
 1. A method comprising: switching on a transistordevice by generating a first conducting channel by driving a first gateelectrode at a first slew rate and, before generating the firstconducting channel, generating a second conducting channel by driving asecond gate electrode at a second slew rate greater than the first slewrate, wherein the second gate electrode is adjacent the first gateelectrode in a current flow direction of the transistor device, whereindriving the first gate electrode comprises increasing a first drivesignal from a first off-level to a first on-level, wherein driving thesecond gate electrode comprises increasing a second drive signal from asecond off-level to a second on-level, and wherein the second off-levelis different from the first off-level.
 2. The method of claim 1, whereinthe transistor device is a field-effect controlled transistor device,wherein generating the first conducting channel comprises generating thefirst conducting channel in a body region, wherein generating the secondconducting channel comprises generating the second conducting channel inthe body region, wherein the first gate electrode is dielectricallyinsulated from the body region by a first gate dielectric, wherein thesecond gate electrode is dielectrically insulated from the body regionby a second gate dielectric, wherein the second gate electrode isseparated from the first gate electrode by a separation layer, andwherein the body region is arranged between a source region and a driftregion, and wherein the drift region is arranged between body region anda drain region.
 3. The method of claim 1, wherein the transistor devicecomprises a HEMT (High Electron Mobility Transistor) device.
 4. Themethod of claim 1, wherein the transistor device comprises a GIT (GateInjection Transistor) device.
 5. The method of claim 4, wherein the GITdevice comprises a first injection gate adjoining the first gateelectrode and a second injection gate adjoining the second gateelectrode.
 6. The method of claim 4, wherein the GIT device comprisesonly one injection gate.
 7. The method of claim 1, wherein driving thefirst gate electrode comprises clamping the second gate electrode to thesecond on-level.
 8. The method of claim 1, further comprising: detectinga change in an operation state of the transistor device, whereindetecting the operation state comprises monitoring at least oneelectrical parameter of the second gate electrode.
 9. The method ofclaim 1, further comprising: switching off a transistor device byinterrupting the first conducting channel via the first gate electrode;and after interrupting the first conducting channel, interrupting thesecond conducting channel via the second gate electrode.
 10. The methodof claim 9, wherein: interrupting the first conducting channel via thefirst gate electrode comprises decreasing a first drive signal from afirst on-level to a first off-level, and interrupting the secondconducting channel via the second gate electrode comprises decreasing asecond drive signal between the second gate electrode and a sourceregion from a second on-level to a second off-level.
 11. A circuitcomprising: a transistor device configured to be switched on bygenerating a first conducting channel by driving a first gate electrodeat a first slew rate, and before generating the first conductingchannel, generating a second conducting channel by driving a second gateelectrode at a second slew rate greater than the first slew rate,wherein the second gate electrode is adjacent the first gate electrodein a current flow direction of the transistor device, wherein drivingthe first gate electrode comprises increasing a first drive signal froma first off-level to a first on-level, wherein driving the second gateelectrode comprises increasing a second drive signal from a secondoff-level to a second on-level, and wherein the second off-level isdifferent from the first off-level.
 12. The circuit of claim 11, whereinthe transistor device is a field-effect controlled transistor device,wherein generating the first conducting channel comprises generating thefirst conducting channel in a body region, wherein generating the secondconducting channel comprises generating the second conducting channel inthe body region, wherein the first gate electrode is dielectricallyinsulated from the body region by a first gate dielectric, wherein thesecond gate electrode is dielectrically insulated from the body regionby a second gate dielectric, wherein the second gate electrode isseparated from the first gate electrode by a separation layer, andwherein the body region is arranged between a source region and a driftregion, and wherein the drift region is arranged between body region anda drain region.
 13. The circuit of claim 11, wherein the transistordevice comprises a HEMT (High Electron Mobility Transistor) device. 14.The circuit of claim 11, wherein the transistor device comprises a GIT(Gate Injection Transistor) device.
 15. The circuit of claim 14, whereinthe GIT device comprises a first injection gate adjoining the first gateelectrode and a second injection gate adjoining the second gateelectrode.
 16. The circuit of claim 14, wherein the GIT device comprisesonly one injection gate.
 17. The circuit of claim 11, wherein drivingthe first gate electrode comprises clamping the second gate electrode tothe second on-level.
 18. The circuit of claim 11, further comprising acircuit configured to detect a change in an operation state of thetransistor device, wherein detecting the operation state comprisesmonitoring at least one electrical parameter of the second gateelectrode.
 19. The circuit of claim 11, wherein the transistor device isconfigured to be switched off by interrupting the first conductingchannel via the first gate electrode, and after interrupting the firstconducting channel, interrupting the second conducting channel via thesecond gate electrode.